The preparation of textured polyester multifilament yarns has been carried out commercially on a worldwide scale for many years. There are numerous well known texturing processes, which involve crimping, looping, coiling or crinkling continuous filamentary yarns. Such texturing processes are commonly used to impart improved properties in textile yarns such as increased stretch, luxurious bulk and improved hand. In one such process, false-twist texturing, yarn is twisted between two points, heated to a heat-setting temperature, cooled and then allowed to untwist. This process imparts the desired texture because deformation caused by the twist has been set in the yarn.
False-twist texturing of polyester yarns originally employed a pin spindle method and has been generally performed on fully oriented yarn. In more recent years, a friction false-twist method was developed for use with partially oriented yarns. False-twist texturing using the friction method permits considerably higher processing speeds than the pin spindle method. In addition, partially oriented yarns can be drawn and textured in a continuous process thereby reducing operational costs. For these reasons, the friction false-twist method is preferable in the production of textured polyester yarns. Such processes have most commonly been carried out using conventional polyester and polyamide yarns.
More recently, attention has been turned to a wider variety of polyester yarns. In particular, more resources have been allocated to commercializing poly(trimethylene terephthalate) yarns for use in the textile industry. In the prior art, only the older and less efficient pin spindle method has been successful for texturing fully oriented poly(trimethylene terephthalate) yarns. Development of a draw-texturing process for partially oriented poly(trimethylene terephthalate) yarn has been impeded by several factors.
The first factor preventing successful commercialization of a continuous draw-texture process for poly(trimethylene terephthalate) has been the lack of a stable partially oriented yarn. After spinning, a partially oriented yarn is typically wound onto a tube, or package. The yarn packages are then stored or sold for use as a feed yarn in later processing operations such as drawing or draw-texturing. A partially oriented yarn package will not be useable in subsequent drawing or draw-texturing processes if the yarn or the package itself are damaged due to aging of the yarns or other damage caused during warehousing or transportation of the yarn package.
Partially oriented poly(ethylene terephthalate) yarns do not typically age very rapidly, and thus they remain suitable for downstream drawing or draw-texturing operations. Such partially oriented yarns are typically spun at speeds of about 3500 yards per minute ("ypm") (3200 meters per minute "mpm"). In the past, attempts to make stable partially oriented poly(trimethylene terephthalate) yarns using a spinning speed in this same range have failed. The resulting partially oriented poly(trimethylene terephthalate) yarns have been found to contract up to about 25% as they crystallize with aging over time. In extreme case, the contraction is so great that the tube is physically damaged by the contraction forces of the yarn. In more common cases, the contraction renders the partially oriented poly(trimethylene terephthalate) yarns unfit for use in drawing or draw-texturing operations. In such cases, the package becomes so tightly wound that the yarn easily breaks as it is unwound from the package.
Another factor impeding the development of a commercially viable continuous draw-texturing process in the prior art has been that the proper processing conditions have not been identified. Efforts toward draw-texturing partially oriented poly(trimethylene terephthalate) yarn via a process similar to that used for polyethylene terephthalate have resulted in poor yarn quality, such as too high or too low bulk and/or excessive broken filaments. In addition to the poor yarn quality, the processing performance has been poor due to excessive texturing breaks. Whenever texturing breaks occur, the draw-texturing process comes to a halt as the yarn must be re-strung in the draw-texturing machine. Such processing inefficiencies result in reduced throughput and increased operating cost. Minor changes in the processing conditions for the friction false-twist method have likewise been unsuccessful.
Other efforts to develop a continuous draw-texture process for poly(trimethylene terephthalate) partially oriented yarns have involved lowering the draw ratio to compensate for the twist induced draw and natural contraction upon crystallization and reducing the tensions across the texturing discs to reduce the level of twist insertion. These efforts have not been successful because they have resulted in a much higher denier in the textured yarn, a poor yarn quality, and a lower operating efficiency. To compensate for these problems, adjustments in feed yarn denier must be made to obtain the desired final denier.
There is therefore a need for a stable partially oriented poly(trimethylene terephthalate) yarn and a continuous draw-texturing process for false-twist texturing the partially oriented yarn. Moreover, the need exists for an economical method for false-twist texturing of a poly(trimethylene terephthalate) partially oriented yarn. The present invention provides such a yarn and process.